The present invention relates to a matrix display device comprising two groups of row electrodes and to the process for controlling this device. It is used in opto-electronics and more particularly in the control of liquid crystal cells used more specifically as converters of electrical data into optical data, in the real time processing of optical images, in the construction of coloured filters particularly usable in colour television and in analog displays.
More specifically, the invention relates to a matrix display device comprising a display cell constituted by two transparent insulating walls and a material comprising a plurality of zones distributed in matrix-like manner, with a first group of p rows of parallel electrodes positioned on one of the two insulating walls and a second group of q columns of parallel electrodes positioned on the other insulating wall. The rows and columns cross one another. An area x.sub.i y.sub.j of the material is defined by the overlap region between row x.sub.i (in which i is an integer which can assume all values between l and p) and column y.sub.j (in which j is an integer between l and q). The bands formed by the columns and rows are such that they can carry signals suitable for the excitation of the material having an optical property dependent on said excitation. This system of electrodes is called a cross-bar system.
Numerous devices of this type are known using, for example, as the sensitive material a liquid crystal film and for which the excitation is electrical. The invention applies particularly advantageously to such devices, but also applies in more general terms to any cross-bar device incorporating a material, whereof one optical property can be modified by means of an electrical excitation. The material can be solid, liquid, amorphous or crystalline. The optical property can be opacity, refractive index, transparency, absorption, diffusion, diffraction, convergence, rotatory power, birefringence, intensity reflected in a given solid angle, etc.
A process for the control of such known display devices consists, for example, in the case of a liquid crystal cell where excitation is of an electrical nature of the application of an alternating voltage V.sub.x to row x.sub.i and a zero voltage to the other rows and the application to the columns y.sub.j of alternating voltages V.sub.yj of the same duration and frequency as voltage V.sub.x, but which are dephased with respect to the latter by a quantity .phi..sub.ji. This phase displacement .phi..sub.ji makes it possible to vary the intensity of the signal to be displayed, i.e. makes it possible to obtain different grey levels.
Such a control process is described in French Patent No. 2,279,123, filed on Feb. 5, 1974 by the present Applicant and entitled "Process for the control of an optical characteristic of a material and analog imager utilizing this process".
This control process applied to devices like those described hereinbefore has the disadvantage of leading to differential accumulation defects.